The concepts herein relate to gaseous fuel combustion for internal combustion engines.
There is a push to utilize natural gas as an engine fuel due to its low cost. Relative to diesel fuel, for instance, natural gas is a lower cost fuel per energy. To take advantage of the lower cost of natural gas, many engines are designed specifically to run on natural gas. Additionally, some engines originally designed to use diesel fuel can be retrofitted to use natural gas as fuel.
Diesel engines have high compression ratios and use compression ignition to ignite the diesel fuel charge. Natural gas is typically ignited with a spark plug. However, the ignition energy from the spark plug does not always effectively ignite the natural gas at high compression ratios, particularly at lean operating conditions. For example, the high velocity of the direct-injected natural gas tends to quench the developing flame kernel. To remedy this, some systems forgo a spark plug and use diesel fuel as a pilot fuel. In other words, these systems inject a small amount of diesel fuel as a pilot fuel early in the compression cycle that auto-ignites from the compression. Natural gas is then by injected and ignited by the combusting pilot fuel. However, a natural gas system using diesel as a pilot fuel requires two fuel systems and associated piping, storage, injectors, etc., which can increase cost, size, complexity and makes retrofitting difficult.
Like reference symbols in the various drawings indicate like elements.